It is important to remember that unless you are building a Passivhaus, the main driver for air testing comes from DEAP BER Calculations.
Small schemes are those including 3 dwellings or less. In this case if it can be demonstrated that during the preceding 12 month period, a dwelling of the same type constructed by the same builder was tested and satisfied the criterion set in paragraph 1.2.4.4 of Part L.
For a dwelling which is a borderline pass, this may be enough to cause a BER failure, and so the client in this case may choose to test that unit and secure a better result.
Which Regs?
The procedure and method for air testing dwellings is set by:
Which Dwellings Do I Need to Test?
This will vary depending on the type of development. General principles are:
Alternatives For Small Schemes
Small schemes are those including 3 dwellings or less. In this case if it can be demonstrated that during the preceding 12 month period, a dwelling of the same type constructed by the same builder was tested and satisfied the criterion set in paragraph 1.2.4.4 of Part L. However, if the assumed air change rate in the calculation of the EPC and CPC using the DEAP methodology is less than the criterion set in paragraph 1.3.4.4, a pressure test to verify this assumed value should be carried out. The guidance given in this sub-section would apply in this situation.
Untested Units
If a dwelling is not tested for any of the reasons above:
Paragraph 1.5.4.7 Where an air permeability value better than the backstop value of 7 m3/hr/m2 at 50 Pascals is claimed for use in DEAP, a test should be performed on each dwelling claiming that value. Therefore any untested dwellings under the BER DEAP regs will effectively take a ‘hit’ which will affect the energy performance of that dwelling.
For a dwelling which is a borderline pass, this may be enough to cause a BER failure, and so the client in this case may choose to test that unit and secure a better result.
Failed Tests
If a dwelling does not meet the required DEAP parameter, remedial works must be carried out and the dwelling re-tested until it complies. It is sometimes possible (depending on your test engineers schedule!) to retest straight away if quick, minor remedial works can be carried out. This may involve caulking or application of sealant for example. Once the test is completed successfully, a further additional dwelling of the same type should be tested, thereby increasing the sample size.